My PSW 12 sub has developed an annoying problem. After a period of time without any audio input static can be heard. The noise can be heard with the power switch in either the off position or auto position. If I switch to the constant on position the static goes away. I have tried different power outlets and positions but there is no change. The static is there even if I remove the audio cable from the sub. I thought about removing the amp section for a physical inspection but there are so many screws on the back I don't which ones hold the panel and which ones are holding components. I don't like the idea of leaving it on all the time. Perhaps a cold solder joint in the amp section? Any ideas?